The excited-state intramolecular proton transfer (ESIPT) reactions of 2-(2′-hydroxyphenyl)benzoxazole (HBO), 5-amino-2-(2′-hydroxyphenyl)benzoxazole (5A-HBO) and 6-amino-2-(2′-hydroxyphenyl)benzoxazole (6A-HBO) were investigated with the time-dependent density functional theory (TD-DFT) method at the B3LYP/6-31G(d,p) theoretical level. The primary bond lengths and infrared (IR) vibrational spectra show that the intramolecular hydrogen bond is significantly strengthened in S₁ state. The Mulliken's charge distribution and the frontier molecular orbitals (MOs) were analyzed. The result is consistent with the ESIPT mechanism proposed by Han and co-workers. Upon photo-excitation, the intramolecular hydrogen bond of 5A-HBO-enol (1.73 Å) and 6A-HBO-enol (1.74 Å) in the S₁ state is weaker than that of HBO-enol (1.69 Å) due to the influence of the amino group in the HBO framework. After vertical excitation to the S₁ state, the electronic density redistributes and migrates from the phenol ring to the benzoxazole ring of HBO. While for 5A-HBO and 6A-HBO, it transfers from the amino-benzoxazole moiety to the phenol ring. The analysis of the potential energy curves of HBO, 5A-HBO and 6A-HBO indicates that the ESIPT process of HBO occurs most easily. It is demonstrated that the presence and the position of the amino group in the HBO framework can change the behavior of the intramolecular hydrogen bonds O–H⋯N in the S₁ state and thus hinder the ESIPT processes to some extent.

The ultrathin metal film with excellent electrical conductivity and high visible-band transmittance has attracted considerable attention as a transparent electrode for the organic light-emitting devices (OLEDs). However, the deficient surface morphology and poor continuity of low thickness evaporated metal films and the surface plasmon-polaritons (SPPs) mode induced energy loss still seriously limit the actual efficiency of OLEDs. In this work, the thermal nanoimprint lithography has been further modified and directly applied to fabricate nanostructures onto the ultrathin Au film. During the imprinting process, the surface smoothness and conductivity of the Au film are obviously optimized with the formation of nanostructures. After integrating proper nanostructures into OLEDs, the photons that trapped by SPPs mode within the device were effectively out-coupled. The current efficiency and luminance have been enhanced 45.3% and 18.1%, respectively. Furthermore, the emitting properties of the OLEDs were also modified by the nanostructures, and the directional transmission capability of output light was significantly improved.